CN114188522A - Microcrystalline graphite/CNT @ C composite material, preparation method thereof and application thereof in lithium secondary battery - Google Patents
Microcrystalline graphite/CNT @ C composite material, preparation method thereof and application thereof in lithium secondary battery Download PDFInfo
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Abstract
The invention belongs to the field of lithium secondary battery cathode materials, and particularly discloses a preparation method of a microcrystalline graphite/CNT @ C composite material2Pretreating in the atmosphere, then placing the pretreated product into liquefied protective gas for quenching while the pretreated product is hot, collecting the quenched product, placing the quenched product into a treatment solution for treatment, and then carrying out solid-liquid separation to obtain microcrystalline graphite A; subjecting the prepared microcrystalline graphite A, a first carbon source and a transition metal source to liquid phase negative pressure treatment, then carrying out solid-liquid separation to obtain a precursor, and carrying out first roasting treatment on the precursor to obtain a microcrystalline graphite core; mixing the microcrystalline graphite core and a second carbon source, and performing second-stage vacuum roasting to obtain the productMicrocrystalline graphite-CNT @ C composite. The invention also comprises the material prepared by the preparation method, the application of the material in a lithium secondary battery and the obtained part. The material prepared by the preparation method has excellent capacity, multiplying power and cycling stability.
Description
Technical Field
The invention belongs to the technical field of lithium battery electrode materials, and particularly relates to a negative electrode active material of a lithium secondary battery.
Background
The microcrystalline graphite is rich in mineral products in China, and is a graphite cathode material with great application potential. The microcrystalline graphite is used as the negative electrode material of the lithium ion battery, and has the advantages of low raw material price, good compatibility with electrolyte, stable cycle performance and good rate capability. However, the impurity content of the natural microcrystalline graphite is high, the crystal form of the natural microcrystalline graphite is not a complete graphite structure, the graphitization degree is low, and the initial coulomb efficiency is low due to an amorphous structure. Therefore, if the microcrystalline graphite is modified by a simple and effective means to comprehensively improve the first coulombic efficiency, reversible specific capacity and cycle life of the microcrystalline graphite, the method has great significance for expanding the market of the natural graphite of the lithium ion battery.
Aiming at the purification research of natural microcrystalline graphite, a mixed acid process is mainly adopted at present, but because the microcrystalline graphite is a naturally formed ore, metal and non-metal impurities in the structure of the microcrystalline graphite are difficult to remove, the existing mixed acid purification process has the problems of common purification effect and large acid consumption. In addition, the surface coating method is also used for improving the first coulomb efficiency of the natural microcrystalline graphite, but the effect is not ideal and cannot reach the level of commercial application. Although the conventional high-temperature graphitization operation higher than 2800 ℃ can realize great improvement of purity and graphitization degree, the conventional high-temperature graphitization operation has the problem of high energy consumption.
Disclosure of Invention
Aiming at the defects of the prior art, the first purpose of the invention is to provide a preparation method of a microcrystalline graphite/CNT @ C composite material, aiming at preparing a high-performance lithium secondary battery negative electrode active material with high value from the microcrystalline graphite.
The second purpose of the invention is to provide the microcrystalline graphite/CNT @ C composite material prepared by the preparation method.
The third purpose of the invention is to provide the application of the microcrystalline graphite/CNT @ C composite material in a lithium secondary battery.
The fourth object of the present invention is to provide a lithium secondary battery comprising the above-mentioned microcrystalline graphite/CNT @ C composite, and a negative electrode thereof.
A preparation method of a microcrystalline graphite/CNT @ C composite material comprises the following steps:
step (1):
adding microcrystalline graphite into the solution containing F2Pretreating in the atmosphere, then placing the pretreated product into liquefied protective gas for quenching while the pretreated product is hot, collecting the quenched product, placing the quenched product into a treatment solution for treatment, and then carrying out solid-liquid separation to obtain microcrystalline graphite A;
the treatment liquid is an aqueous solution dissolved with HF and inorganic acid;
step (2):
subjecting the prepared microcrystalline graphite A, a first carbon source and a transition metal source to liquid phase negative pressure treatment, then carrying out solid-liquid separation to obtain a precursor, and carrying out first roasting treatment on the precursor to obtain a microcrystalline graphite core;
and (3):
and mixing the microcrystalline graphite core and a second carbon source, and performing second-stage vacuum roasting to obtain the microcrystalline graphite-CNT @ C composite material.
The research of the invention finds that the combination of fluorine gas pretreatment, liquefied gas quenching, treatment liquid treatment, liquid phase negative pressure treatment, first roasting and second stage vacuum roasting processes is innovatively adopted, so that the synergy can be unexpectedly realized, and the microcrystalline graphite/CNT @ C composite material which is prepared into a microcrystalline graphite and carbon nano tube composite core and is coated with a carbon layer on the surface of the core can be prepared. Researches show that the material prepared by the preparation method has excellent capacity, multiplying power and cycling stability.
In the invention, the microcrystalline graphite can be natural microcrystalline graphite or microcrystalline graphite waste, and the median particle size is not particularly required, and can be 8-15 μm, for example.
In the invention, the microcrystalline graphite is innovatively placed in fluorine gas for gas-solid pretreatment, so that the structure can be subjected to intercalation and layer expansion, the microstructure is reformed, abnormal active sites are avoided, the transformation of impurity elements is facilitated, and the subsequent liquefied gas quenching-treatment liquid treatment is further matched, so that the solidification and the microstructure improvement can be facilitated, and not only is the selective removal of useless impurities promoted in a synergistic manner facilitated, and the preparation of a high-performance negative electrode material is facilitated.
In the present invention, F is contained2The atmosphere being pure F2Or F2Mixed gas with protective gas;
preferably, said F-containing compound2In the atmosphere, F2Is greater than or equal to 1% by volume; preferably 1 to 10 vol%;
preferably, in the step (1), the temperature of the pretreatment is 300-600 ℃; preferably 300-500 ℃; further preferably 400-500 ℃;
preferably, the pretreatment time is 0.5-2 h.
In the invention, under the gas-solid heat treatment of the fluorine gas, a liquefied gas quenching process is further matched, the microstructure can be further regulated and controlled by means of the instantaneous gasification effect of liquefied gas, and the separation of impurities is facilitated; can improve the performance of the microcrystalline graphite synergistically.
Preferably, the liquefied protective gas is at least one of liquid nitrogen and liquefied carbon dioxide;
preferably, the temperature of the pretreatment product entering the liquefied protective gas is 250-600 ℃. For example, the pretreated product can be placed directly in the liquefied protective gas without cooling.
In the present invention, the quenched material is then treated in a treatment liquid. The research of the invention finds that the combination of the inorganic acid and the HF is helpful for cooperating with other processes to improve the electrochemical performance of the prepared material.
In the treatment solution, the inorganic acid is at least one of HCl, sulfuric acid and nitric acid;
preferably, the HF in the process fluid may be an analytically pure material or may be derived from pre-treated off-gas.
Preferably, the concentration of HF in the treatment liquid is 0.01-2M; the concentration of the inorganic acid is 0.1-2M, preferably 0.2-1M;
preferably, the treatment fluid can also be added with an auxiliary additive, and the auxiliary additive is a compound which can be mutually dissolved with water and stably exists in acid, and is preferably at least one of salt and alcohol; preferably, the salt is at least one of an alkali metal salt and an alkaline earth metal salt; the alcohol is a C1-C6 unit or multi-element solvent;
preferably, the weight ratio of water to auxiliary additives in the treatment fluid is 1: 0.1 to 10;
preferably, the solid-liquid ratio of the quenched microcrystalline graphite to the treatment liquid is 0.5-2: 10 (g/ml).
The temperature in the treatment process is not particularly required, and may be, for example, 15 to 80 ℃.
Preferably, the time of the treatment process is 0.5-4 h.
In the invention, the product of fluorine gas pretreatment, liquefied gas quenching and treatment liquid treatment, the subsequent first carbon source and the transition metal source are subjected to liquid phase negative pressure treatment, which is beneficial to further preparing the material with the special structure and further preparing the high-performance negative electrode material.
Preferably, the first carbon source is one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon and the like;
preferably, the mass ratio of the microcrystalline graphite a to the first carbon source is 100: 1-8, preferably 100: 2-6;
preferably, the transition metal source is a water-soluble salt of a transition metal; preferably at least one water-soluble salt of chloride, nitrate and oxalate of transition metal; the preferable transition metal element is at least one of iron, cobalt and nickel;
preferably, the weight ratio of microcrystalline graphite a to transition metal source is 100: 2-10, preferably 100: 4-6;
preferably, the solvent in the liquid phase vacuum treatment process is water or a homogeneous mixed solvent of water and an organic solvent, wherein the organic solvent is at least one of C1-C4 alcohol and toluene;
preferably, in the liquid phase vacuum treatment process, the solid-liquid ratio is 1: 3-10 g/ml; the solid-liquid ratio refers to the weight ratio of the microcrystalline graphite A to the volume ratio of the liquid-phase solution.
Preferably, the vacuum degree in the liquid phase vacuum treatment stage is 50-500 Pa, preferably 50-300 Pa;
preferably, the liquid phase vacuum treatment time is 2-6 h;
preferably, the liquid phase vacuum treatment system is subjected to freeze drying treatment to obtain the precursor.
In the invention, the precursor is subjected to low-temperature first roasting treatment in advance, and then is matched with subsequent carbon-blending second-stage vacuum roasting treatment, so that the electrochemical performance of the prepared material is improved in a synergistic manner.
Preferably, the atmosphere of the first roasting process is one or more of hydrogen, argon, nitrogen and helium.
Preferably, the temperature of the first roasting is 200-400 ℃, and preferably 200-300 ℃. The first roasting time is 0.5-4 h, preferably 1-2 h.
Preferably, the second carbon source is one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon and the like.
Preferably, the microcrystalline graphite core and the second carbon source may be mixed based on existing means.
Preferably, the weight ratio of the microcrystalline graphite core to the second carbon source is 100: 5-12, preferably 100: 5-10;
preferably, in the second stage of vacuum roasting, the system is heated to 350-450 ℃ and then set to be in a vacuum state.
Preferably, the vacuum degree of the second-stage vacuum roasting is less than or equal to 500Pa, preferably 10-500 Pa, and further preferably 50-300 Pa;
preferably, the temperature of the second-stage vacuum roasting is 900-1250 ℃;
preferably, the time of the second stage of vacuum roasting is 2-6 h;
preferably, the second-stage vacuum roasting product is placed in the treatment liquid for treatment, and then is washed and dried to obtain the microcrystalline graphite/CNT @ C composite material.
The preferred preparation method comprises the following steps:
step (a): heating the natural microcrystalline graphite to a certain temperature, and introducing fluorine gas for pretreatment for a certain time; the fluorine gas may further contain at least one of inert gases such as nitrogen, argon and helium, and preferably argon. The content of the fluorine gas in the atmosphere is 1 to 10 vol%. The fluorine gas treatment temperature is 300-600 ℃; the temperature is preferably 400-500 ℃; the time for fluorine gas pretreatment is 0.5-2 h.
Step (b): directly putting the pretreated microcrystalline graphite obtained in the previous step into liquid nitrogen for quenching while the pretreated microcrystalline graphite is hot, then putting the powder into a treatment solution for stirring reaction, performing solid-liquid separation, keeping a liquid phase for later use, continuously washing the obtained slurry to be neutral, and performing drying treatment to obtain microcrystalline graphite A; the treatment solution in the step (b) contains water, alcohols, HF and conventional acids (inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid and the like), the concentration of the conventional acids is 0.2-2M, and the volume ratio of the water to the alcohols is 1: 0.1-10, solid-to-liquid ratio (mg/ml) of 0.5-2: 10, stirring and reacting for 0.5-4 h. And (f) after the stirring reaction is finished, performing conventional solid-liquid separation, slurry washing and drying, wherein the separated liquid is reserved for the purification in the step (f).
Step (b): uniformly stirring the dried microcrystalline graphite material (microcrystalline graphite A), a carbon source precursor (a first carbon source), a transition metal salt and a solvent (such as water) under a negative pressure condition, and then putting the mixture into a freeze dryer for removing the solvent to obtain dry powder (precursor); the carbon source precursor in the step (c) can be one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon and the like, and the mass ratio of the dry microcrystalline graphite material to the carbon source precursor is 100: 1-8; the transition metal salt is one or more of chloride, nitrate, oxalate and the like of iron, cobalt and nickel, and the mass ratio of the dry microcrystalline graphite material to the transition metal salt is 100: 2-10; the solvent is a liquid substance capable of dissolving the transition metal salt, and can be water or a mixed solution of water and organic matters such as alcohol, toluene and the like; in the system (microcrystalline graphite, carbon source, transition metal salt and solvent), the solid-to-liquid ratio (mg/ml) is 1: 3 to 10. The stirring under the negative pressure condition can be carried out in a conventional vacuum stirring kettle; the freeze-drying operation is a freeze-drying operation and can be carried out in a conventional freeze dryer.
Step (d): carrying out first low-temperature heat treatment (first roasting) on the dried powder (precursor) to obtain a microcrystalline graphite core; and (d) performing primary low-temperature treatment at 200-400 ℃ for 0.5-4 h in one or more of hydrogen, argon, nitrogen and helium.
A step (e): uniformly mixing the material (microcrystalline graphite core) obtained in the previous step and a carbon source precursor (second carbon source), and then carrying out second vacuum heat treatment; the carbon source precursor in the step (e) can be one or more of asphalt, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon and the like, and the mass ratio of the microcrystalline graphite material to the carbon source precursor is 100: 5-12; the realization process can be conventional mixing and sintering, and can also be spray pyrolysis; and the second heat treatment is to raise the temperature to 350-450 ℃ at a certain heating rate, then carry out vacuum pumping operation to maintain the vacuum degree of the system at 10-500 Pa, then carry out temperature programming on the system to 900-1250 ℃, carry out treatment for 2-6 h under the condition of negative pressure, and carry out natural cooling after the heat treatment atmosphere is one or more of hydrogen, argon, nitrogen and helium.
Step (f): and (3) putting the powder subjected to the heat treatment in the second step into the water-containing pretreatment solvent (the treatment solution in the step (b) or the used treatment solution) in the step (b) again, and after the stirring reaction is finished, performing conventional solid-liquid separation, drying and scattering to finally obtain the high-performance natural microcrystalline graphite cathode material. And (f) purifying, namely placing the powder obtained after heat treatment into the treatment liquid obtained in the step (b), wherein the solid-to-liquid ratio (mg/ml) is 1-3: 10, the stirring temperature is 30-80 ℃, and the stirring reaction time is 2-6 h.
In the prior art, natural microcrystalline graphite is usually purified by a mixed acid method or a high-temperature heat treatment method, but the method has high energy consumption and large consumption of acid and water; and because the natural microcrystalline graphite is a naturally formed ore, impurity elements in the structure of the natural microcrystalline graphite are difficult to completely remove, so that the purification efficiency is not high and the purification cost is high. Therefore, the invention provides the preparation method, which adopts fluorine gas to carry out gas-solid pretreatment in an innovative way, so that the layer expansion and intercalation modification can be realized, the structural defects can be reduced, the active sites with abnormal surfaces can be reduced, and the transformation of impurities can be facilitated so as to facilitate the subsequent efficient removal. Further matching with subsequent quenching of liquefied protective gas-treatment liquid treatment, the fluorinated microstructure can be subjected to solidification and microstructure regulation, electrochemical unfavorable impurities can be removed in a synergistic manner, and the surface property and wettability of the material can be improved. And finally, performing subsequent liquid-phase negative pressure first-stage carbon distribution-low-temperature first roasting and second-stage carbon distribution-second-stage vacuum roasting on the treated microcrystalline graphite to construct a microcrystalline graphite-CNT composite core and a new material for densely coating a carbon layer on the surface of the core, wherein the new material can show excellent capacity, multiplying power and cycling stability.
The invention also provides the microcrystalline graphite/CNT @ C composite material prepared by the preparation method, which comprises an inner core and an outer shell, wherein the inner core is microcrystalline graphite particles treated by the treatment method and is dispersed in a carbon nano tube cluster; the shell is a uniform and compact carbonization zone; the shell is anchored on the surface of the inner core, and the natural microcrystalline graphite in the inner core has the characteristics of large interlayer spacing, high purity and anisotropy. The research of the invention finds that the natural microcrystalline graphite material has the advantages of high first coulombic efficiency, good rate capability, high capacity, long service life and the like.
The microcrystalline graphite/CNT @ C composite material has the fixed carbon content higher than 99.96 percent and the total specific surface area of 1.2-3.5m2/g。
The invention also provides an application of the microcrystalline graphite/CNT @ C composite material prepared by the preparation method, and the microcrystalline graphite/CNT @ C composite material is used as a negative electrode active material of a lithium secondary battery, particularly a power type lithium ion battery.
The composite material is preferably used as a negative active material and is used for being compounded with a conductive agent and a binder to prepare a negative material. The conductive agent and the binder are all materials known in the industry.
In a further preferable application, the negative electrode material is arranged on the surface of a negative electrode current collector and used for preparing a negative electrode. The negative electrode may be formed by applying the negative electrode material of the present invention to a current collector by a conventional method, for example, by a coating method. The current collector is any material known in the industry.
In a further preferred application, the negative electrode, the positive electrode, the separator and the electrolyte are assembled into a lithium secondary battery.
A lithium secondary battery comprising the microcrystalline graphite/CNT @ C composite material prepared by the preparation method.
The lithium secondary battery, the negative pole piece comprises the microcrystalline graphite/CNT @ C composite material.
Preferably, the lithium secondary battery is a lithium ion battery or a lithium metal battery.
The technical scheme of the invention has the beneficial effects that:
(1) the method combines the processes of fluorine gas pretreatment, liquefied protective gas quenching, treatment liquid treatment, liquefied vacuum first-stage carbon preparation, first roasting treatment, second-stage carbon preparation and second-stage vacuum roasting on the microcrystalline graphite, can unexpectedly regulate and control the structure of the microcrystalline graphite, regulates and controls the chemical characteristics of the microcrystalline graphite, and is favorable for preparing the negative active material with the special double-carbon structure and excellent capacity, multiplying power and cycle performance.
(2) The temperature in the heat treatment process is not more than 1250 ℃, and the preparation process is environment-friendly without ultrahigh temperature treatment.
(3) The method has the advantages of wide raw material source, simple operation, easy realization, strong controllability, easy realization of large-scale production and good practical prospect.
(4) The method has the greatest advantage of realizing high-quality utilization of the natural microcrystalline graphite.
Drawings
FIG. 1 is an SEM image of a sample obtained in example 1 after treatment with fluorine gas and quenching with liquid nitrogen.
FIG. 2 is an SEM photograph of the final sample obtained in example 1.
FIG. 3 is a TEM image of the final sample obtained in example 1.
Detailed Description
The specific procedures of the present invention are illustrated below by way of examples, it being understood that these examples are intended to illustrate the invention and are not intended to limit the scope of the invention in any way. Various procedures and methods not described in detail herein are conventional methods well known in the art.
Example 1
Step (1): placing natural microcrystalline graphite (D50 ═ 13.5 μm) in an atmosphere furnace, heating to 300 ℃ at 5 ℃/min, introducing 200ml/min fluorine gas (2% vol, and the balance being nitrogen), preserving heat for pretreatment for 0.5h under the condition, and putting the obtained material into liquid nitrogen while the material is hot to obtain a quenching material; introducing tail gas in the treatment process into a 0.2M hydrochloric acid solution (the volume ratio of water to ethanol is 1: 1) pretreatment solution to obtain a treatment solution;
step (2): and (3) quenching materials in a solid-to-liquid ratio of 1: dispersing 10(g/mL) in the treatment solution, stirring and reacting for 1h at 40 ℃, filtering, washing slurry and drying materials to obtain microcrystalline graphite A, and reserving the acid solution after solid-liquid separation for later use.
And (3): according to the solid-liquid ratio of 1: 10(g/ml), drying the obtained dried microcrystalline graphite material (microcrystalline graphite A), polyacrylonitrile and ferric nitrate according to the mass ratio of 100: 2: 4, uniformly dispersing in water, uniformly stirring under the condition of negative pressure (200Pa), and then placing in a freeze dryer for solvent removal to obtain dry powder (precursor);
and (4): roasting in the first stage:
and (3) placing the obtained dry powder (precursor) in an atmosphere furnace, heating to 200 ℃ at the speed of 10 ℃/min under the protection of argon atmosphere, preserving heat (first-stage roasting) for 1h, and naturally cooling to room temperature.
And (5): and (3) second-stage vacuum roasting:
and mixing the obtained material (microcrystalline graphite core) and the asphalt according to the mass ratio of 100:5, uniformly mixing, heating to 400 ℃ at the heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 10Pa, heating to 1000 ℃ at the heating rate of 10 ℃/min, preserving heat for 2h under the condition, and naturally cooling to room temperature. And (3) placing the powder obtained by the heat treatment into the reserved treatment liquid (the treatment liquid in the step (1) or (2)) again, and mixing the powder obtained by the heat treatment in a solid-liquid ratio of 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area is 1.5m2The fixed carbon content was 99.97% per gram. According to GB/T24332009, the graphite electrode is used as a working electrode, metal lithium is used as a negative electrode, and 1mol/L LiPF6The EC/EMC (volume ratio is 1: 1) of the battery is electrolyte, the PE-PP composite membrane is a diaphragm, the CR2025 button cell is assembled in a dry glove box filled with argon, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 362mAh/g, the coulombic efficiency is 96%, and the capacity retention rate is 98% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 93.2%.
Example 2
Step (1): placing natural microcrystalline graphite (D50 is 9.5 mu m) in an atmosphere furnace, heating to 400 ℃ at the speed of 5 ℃/min, introducing 200ml/min fluorine gas (5% vol, and the balance being nitrogen), preserving the temperature for 1h under the condition, putting the obtained material into liquid nitrogen while the material is hot, taking out the cooled material, and obtaining a quenched material; introducing tail gas in the treatment process into a 0.5M nitric acid solution (the volume ratio of water to ethanol is 1: 2) pretreatment solution to obtain a treatment solution;
step (2): and (3) quenching materials in a solid-to-liquid ratio of 1: dispersing 10g/ml in the above treatment solution, stirring at 50 deg.C for 2 hr, performing conventional solid-liquid separation, washing slurry, and oven drying to obtain microcrystalline graphite A, and keeping the acid solution after solid-liquid separation for use.
And (3): according to the solid-liquid ratio of 1: 5(g/ml), drying the obtained dried microcrystalline graphite material (microcrystalline graphite A), polyacrylonitrile and ferric nitrate according to the mass ratio of 100: 4: 4, uniformly dispersing in water, stirring uniformly under the condition of negative pressure (200Pa), and then placing in a freeze dryer for solvent removal to obtain dry powder to obtain a precursor;
and (4): and (3) placing the obtained dry powder (precursor) in an atmosphere furnace, heating to 300 ℃ at a speed of 10 ℃/min under the protection of argon atmosphere, preserving the temperature for 2h, and naturally cooling to room temperature.
And (5):
and mixing the obtained material and polyaniline according to a mass ratio of 100: 6, after mixing uniformly, heating to 400 ℃ at a heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 20Pa, heating to 1100 ℃ at a heating rate of 10 ℃/min, preserving heat for 2h under the condition, and naturally cooling to room temperature. And putting the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent again, wherein the solid-liquid ratio is 1: 5 stirring at 50 deg.C for 4h, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area was 2.1m2/g, and the fixed carbon content was 99.98%. According to GB/T2433integral 2009, a CR2025 button cell is assembled in a dry glove box filled with argon by taking a graphite electrode as a working electrode, metal lithium as a negative electrode, EC/EMC (volume ratio 1: 1) of 1mol/L LiPF6 as electrolyte and a PE-PP composite membrane as a diaphragm, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 361mAh/g, the coulombic efficiency is 95%, and the capacity retention ratio is 97% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 93.6%.
Example 3
Placing natural microcrystalline graphite (D50 ═ 10.5 μ M) in an atmosphere furnace, heating to 500 ℃ at 5 ℃/min, introducing 200ml/min fluorine (5% vol, and the balance argon), introducing tail gas into 1M sulfuric acid solution (the volume ratio of water to methanol is 1: 1) pretreatment solution, preserving heat for 0.5h under the conditions, putting the obtained material into liquid nitrogen while hot, taking out the cooled material, and mixing the obtained material with the following solid-liquid ratio of 0.5: 10(g/ml), dispersing the acid liquor into the pretreatment solution, carrying out stirring reaction for 1h at 40 ℃, carrying out conventional solid-liquid separation, slurry washing and material drying, and reserving the acid liquor after solid-liquid separation for later use. According to the solid-liquid ratio of 1: 10(g/ml), drying the dried microcrystalline graphite material, phenolic resin and nickel nitrate according to the mass ratio of 100: 5: 5, uniformly dispersing in water, uniformly stirring under the condition of negative pressure (150Pa), and then placing in a freeze dryer for solvent removal to obtain dry powder; and (3) placing the obtained dry powder in an atmosphere furnace, heating to 300 ℃ at a speed of 10 ℃/min under the protection of argon atmosphere, preserving the temperature for 2h, and naturally cooling to room temperature. And mixing the obtained material and asphalt according to a mass ratio of 100: 6, after mixing uniformly, heating to 400 ℃ at a heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 50Pa, heating to 1200 ℃ at a heating rate of 10 ℃/min, preserving heat for 2h under the condition, and naturally cooling to room temperature. And putting the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent again, wherein the solid-liquid ratio is 1: stirring at 60 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area was 1.8m2/g, and the fixed carbon content was 99.98%. According to GB/T2433integral 2009, a CR2025 button cell is assembled in a dry glove box filled with argon by taking a graphite electrode as a working electrode, metal lithium as a negative electrode, EC/EMC (volume ratio 1: 1) of 1mol/L LiPF6 as electrolyte and a PE-PP composite membrane as a diaphragm, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 364mAh/g, the coulombic efficiency is 95%, and the capacity retention ratio is 96% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 93.9%.
Example 4
Placing natural microcrystalline graphite (same as example 1) in an atmosphere furnace, heating to 300 ℃ at a speed of 5 ℃/min, introducing 200ml/min fluorine gas (8% vol, and the balance helium gas), introducing tail gas into a 0.2M nitric acid solution (the volume ratio of water to ethanol is 1: 1) pretreatment solution, preserving heat for 0.5h under the condition, putting the obtained material into liquid nitrogen while hot, taking out the cooled material, and mixing the obtained material with the following components in a solid-to-liquid ratio of 1: 10(g/ml), dispersing the acid liquor into the pretreatment solution, carrying out stirring reaction for 1h at 40 ℃, carrying out conventional solid-liquid separation, slurry washing and material drying, and reserving the acid liquor after solid-liquid separation for later use. According to the solid-liquid ratio of 1: 10(g/ml), drying the obtained dried microcrystalline graphite material, polypyrrole and nickel oxalate according to the mass ratio of 100: 6: 4, uniformly dispersing in water, uniformly stirring under the condition of negative pressure (300Pa), and then placing in a freeze dryer for solvent removal to obtain dry powder; and (3) placing the obtained dry powder in an atmosphere furnace, heating to 200 ℃ at a speed of 10 ℃/min under the protection of argon atmosphere, preserving heat for 1h, and naturally cooling to room temperature. And mixing the obtained material and polyaniline according to a mass ratio of 100: 10, after uniformly mixing, heating to 400 ℃ at the heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 100Pa, heating to 1250 ℃ at the heating rate of 10 ℃/min, preserving heat for 2h under the condition, and naturally cooling to room temperature. And putting the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent again, wherein the solid-liquid ratio is 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area was 2.4m2/g, and the fixed carbon content was 99.98%. According to GB/T2433integral 2009, a CR2025 button cell is assembled in a dry glove box filled with argon by taking a graphite electrode as a working electrode, metal lithium as a negative electrode, EC/EMC (volume ratio 1: 1) of 1mol/L LiPF6 as electrolyte and a PE-PP composite membrane as a diaphragm, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 359mAh/g, the coulombic efficiency is 96%, and the capacity retention ratio is 97% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 94.2%.
Example 5
Placing natural microcrystalline graphite (same as example 1) in an atmosphere furnace, heating to 500 ℃ at a speed of 5 ℃/min, introducing 200ml/min fluorine gas (10% vol, and the balance being nitrogen), introducing tail gas into a 0.2M nitric acid solution (the volume ratio of water to ethanol is 1: 1) pretreatment solution, preserving heat for 0.5h under the conditions, putting the obtained material into liquid nitrogen while hot, taking out the cooled material, and mixing the obtained material in a solid-to-liquid ratio of 1: 10(g/ml), dispersing the acid liquor into the pretreatment solution, carrying out stirring reaction for 1h at 40 ℃, carrying out conventional solid-liquid separation, slurry washing and material drying, and reserving the acid liquor after solid-liquid separation for later use. According to the solid-liquid ratio of 1: 10(g/ml), drying the obtained dried microcrystalline graphite material, glucose and nickel acetate according to the mass ratio of 100: 6: 5, uniformly dispersing the mixture in water, uniformly stirring the mixture under the condition of negative pressure (200Pa), and then putting the mixture into a freeze dryer for removing a solvent to obtain dry powder; and (3) placing the obtained dry powder in an atmosphere furnace, heating to 200 ℃ at a speed of 10 ℃/min under the protection of argon atmosphere, preserving heat for 1h, and naturally cooling to room temperature. And mixing the obtained material and asphalt according to a mass ratio of 100: 8, after uniformly mixing, heating to 400 ℃ at the heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 300Pa, heating to 900 ℃ at the heating rate of 10 ℃/min, preserving heat for 4h under the condition, and naturally cooling to room temperature. And putting the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent again, wherein the solid-liquid ratio is 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area was 2.6m2/g, and the fixed carbon content was 99.97%. According to GB/T2433integral 2009, a CR2025 button cell is assembled in a dry glove box filled with argon by taking a graphite electrode as a working electrode, metal lithium as a negative electrode, EC/EMC (volume ratio 1: 1) of 1mol/L LiPF6 as electrolyte and a PE-PP composite membrane as a diaphragm, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 363mAh/g, the coulombic efficiency is 96%, and the capacity retention ratio is 98% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 92.9%.
Example 6
Placing natural microcrystalline graphite (same as example 1) in an atmosphere furnace, heating to 300 ℃ at a speed of 5 ℃/min, introducing 200ml/min fluorine gas (8% vol, and the balance being nitrogen), introducing tail gas into 0.2M hydrochloric acid solution (the volume ratio of water to ethanol is 1: 1) pretreatment solution, preserving heat for 0.5h under the conditions, putting the obtained material into liquid nitrogen while hot, taking out the cooled material, and mixing the obtained material with the mixed solution in a solid-to-liquid ratio of 1: 10(g/ml), dispersing the acid liquor into the pretreatment solution, carrying out stirring reaction for 1h at 40 ℃, carrying out conventional solid-liquid separation, slurry washing and material drying, and reserving the acid liquor after solid-liquid separation for later use. According to the solid-liquid ratio of 1: 10(g/ml), drying the obtained dried microcrystalline graphite material, polypropylene and ferric nitrate according to the mass ratio of 100: 2: 4, uniformly dispersing in water, uniformly stirring under the condition of negative pressure (200Pa), and then placing in a freeze dryer for solvent removal to obtain dry powder; and (3) placing the obtained dry powder in an atmosphere furnace, heating to 200 ℃ at a speed of 10 ℃/min under the protection of argon atmosphere, preserving heat for 1h, and naturally cooling to room temperature. And mixing the obtained material and asphalt according to a mass ratio of 100: 12, after uniformly mixing, heating to 400 ℃ at the heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 500Pa, heating to 1250 ℃ at the heating rate of 10 ℃/min, preserving heat for 1h under the condition, and naturally cooling to room temperature. And putting the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent again, wherein the solid-liquid ratio is 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The performance test result of the material is as follows: the total specific surface area was 3.2m2/g, and the fixed carbon content was 99.98%. According to GB/T2433integral 2009, a CR2025 button cell is assembled in a dry glove box filled with argon by taking a graphite electrode as a working electrode, metal lithium as a negative electrode, EC/EMC (volume ratio 1: 1) of 1mol/L LiPF6 as electrolyte and a PE-PP composite membrane as a diaphragm, electrochemical performance detection is carried out in a voltage range of 0.001-2.0V at room temperature, when the charge-discharge test current density is 0.2C, the first reversible capacity is 367mAh/g, the coulombic efficiency is 96%, and the capacity retention ratio is 98% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 94.1%.
Comparative example 1:
the only difference compared with example 1 is that the pretreatment process in step (1) is performed in nitrogen atmosphere and does not contain fluorine gas, and other steps and parameters and electrochemical test conditions are the same as those in example 1.
The performance test result of the material is as follows: the fixed carbon content was 87.3%. Performing electrochemical measurement according to the method of the embodiment 1, when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 232mAh/g, the coulombic efficiency is 76%, and the capacity retention rate is 63% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 32.9%.
Comparative example 2:
compared with the example 1, the difference is that in the step (1), liquid nitrogen quenching is not adopted, but a water cooling process is adopted (namely normal temperature water is adopted to replace the liquid nitrogen), and the difference is as follows: putting the obtained material into normal-temperature water while the material is hot, then filtering and drying the material, and then carrying out the following steps: the other procedures and parameters and electrochemical test conditions were the same as in example 1.
The electrochemical test results are as follows: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 237mAh/g, the coulombic efficiency is 63 percent, and the capacity retention rate is 61 percent after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 42.8%.
Comparative example 3:
compared with the example 1, the difference is that in the step (1), liquid nitrogen quenching is not adopted, but natural cooling is adopted, and the difference steps are as follows: the pretreated material was naturally cooled to room temperature, followed by the step (2) and subsequent steps, which were the same as in example 1, and electrochemical measurements were performed as in example 1.
The electrochemical results are: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 211mAh/g, the coulombic efficiency is 67%, and the capacity retention rate is 62% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 57.9%.
Comparative example 4:
the difference from example 1 is only that the treatment liquid does not contain HF, that is, the treatment of steps (2) and (5) is carried out without adsorbing the off-gas of step (1) with a 0.2M hydrochloric acid solution, but directly with a 0.2M hydrochloric acid solution (water to ethanol volume ratio of 1: 1, no HF contained) as the treatment liquid. The other steps and parameters and the electrochemical measurement method were the same as in example 1.
The electrochemical results are: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 251mAh/g, the coulombic efficiency is 77%, and the capacity retention rate is 68% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 32.9%.
Comparative example 5:
the only difference from example 1 is that step (3) was not subjected to a liquid phase treatment under negative pressure but was subjected to a treatment under normal pressure, and the other operations, parameters and measurement methods were the same as those of example 1.
The electrochemical results are: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 181mAh/g, the coulombic efficiency is 56%, and the capacity retention rate is 42% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 32.1%.
Comparative example 6:
the only difference compared to example 1 is that the first stage firing of step (4) is not performed, but the precursor is directly subjected to the vacuum firing of step (5).
The distinguishing steps are as follows:
mixing a precursor and asphalt according to a mass ratio of 100:5, uniformly mixing, heating to 400 ℃ at the heating rate of 5 ℃/min, vacuumizing to maintain the vacuum degree of the system at 10Pa, heating to 1000 ℃ at the heating rate of 10 ℃/min, preserving heat for 2h under the condition, and naturally cooling to room temperature. Placing the powder obtained by the heat treatment into the aqueous pretreatment (treatment liquid) solvent reserved before again, and carrying out the solid-liquid ratio of 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The electrochemical results are: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 155mAh/g, the coulombic efficiency is 46%, and the capacity retention rate is 51% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 38.9%.
Comparative example 7:
the only difference compared to example 1 is that step (5) does not involve a second stage firing under vacuum.
The distinguishing step (5) is as follows: mixing the obtained material (microcrystalline graphite core) and the asphalt according to the mass ratio of 100:5, uniformly mixing, heating to 400 ℃ at a heating rate of 5 ℃/min, heating to 1000 ℃ at a heating rate of 10 ℃/min, carrying out heat preservation treatment for 2h under the condition, and naturally cooling to room temperature. Placing the powder obtained by the heat treatment into the previously reserved aqueous pretreatment solvent (treatment liquid) again, and mixing the mixture in a solid-liquid ratio of 1: stirring at 40 deg.C for 2 hr, performing conventional solid-liquid separation, drying, and scattering.
The electrochemical results are: when the current density of the charge and discharge test is 0.2C, the first reversible capacity is 342mAh/g, the coulombic efficiency is 91%, and the capacity retention rate is 90% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 23.1%.
Comparative example 8
The only difference compared to example 1 is that in step (3), no polyacrylonitrile was added. The other procedures, operations, parameters and measurement methods were the same as in example 1.
When the current density of the charge and discharge test is 0.2C, the first reversible capacity is 252mAh/g, the coulombic efficiency is 62%, and the capacity retention rate is 45% after 500 cycles; the material is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 31.2%.
Comparative example 9
The only difference compared to example 1 is that in step (3), no iron nitrate was added. The other procedures, operations, parameters and measurement methods were the same as in example 1.
When the current density of the charge and discharge test is 0.2C, the first reversible capacity is 224mAh/g, the coulombic efficiency is 53%, and the capacity retention rate is 41% after 500 cycles; the lithium ion battery is rapidly charged and discharged under the condition of 5C, and the multiplying power capacity ratio of 5C/0.2C is 28.7%.
Claims (10)
1. The preparation method of the microcrystalline graphite/CNT @ C composite material is characterized by comprising the following steps of:
step (1):
adding microcrystalline graphite into the solution containing F2Pretreating in the atmosphere, then placing the pretreated product into liquefied protective gas for quenching while the pretreated product is hot, collecting the quenched product, placing the quenched product into a treatment solution for treatment, and then carrying out solid-liquid separation to obtain microcrystalline graphite A;
the treatment liquid is an aqueous solution dissolved with HF and inorganic acid;
step (2):
subjecting the prepared microcrystalline graphite A, a first carbon source and a transition metal source to liquid phase negative pressure treatment, then carrying out solid-liquid separation to obtain a precursor, and carrying out first roasting treatment on the precursor to obtain a microcrystalline graphite core;
and (3):
and mixing the microcrystalline graphite core and a second carbon source, and performing second-stage vacuum roasting to obtain the microcrystalline graphite-CNT @ C composite material.
2. The method of making a microcrystalline graphite/CNT @ C composite of claim 1, comprising F2The atmosphere being pure F2Or F2Mixed gas with protective gas;
preferably, said F-containing compound2In the atmosphere, F2Is greater than or equal to 1% by volume; preferably 1 to 10 vol%;
preferably, in the step (1), the temperature of the pretreatment is 300-600 ℃; preferably 400-500 ℃;
preferably, the pretreatment time is 0.5-2 h.
3. The method of making a microcrystalline graphite/CNT @ C composite material of claim 1, wherein the liquefied shielding gas is at least one of liquid nitrogen and liquefied carbon dioxide;
preferably, the temperature of the pretreatment product entering the liquefied protective gas is 250-600 ℃.
4. The method of making a microcrystalline graphite/CNT @ C composite of claim 1, wherein the inorganic acid in the treatment fluid is at least one of HCl, sulfuric acid, nitric acid;
preferably, in the treatment solution, the HF is derived from pretreated tail gas;
preferably, the concentration of HF in the treatment liquid is 0.01-2M; the concentration of the inorganic acid is 0.1-2M;
preferably, the treatment fluid further contains an auxiliary additive, wherein the auxiliary additive is a compound which can be mutually dissolved with water and stably exists in acid, and is preferably at least one of salt and alcohol; preferably, the salt is at least one of an alkali metal salt and an alkaline earth metal salt; the alcohol is a C1-C6 unit or multi-element solvent;
preferably, the weight ratio of water to auxiliary additives in the treatment fluid is 1: 0.1 to 10;
preferably, the time of the treatment process is 0.5-4 h.
5. The method of claim 1, wherein the first carbon source is one or more of pitch, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon, etc.;
preferably, the mass ratio of the microcrystalline graphite a to the first carbon source is 100: 1-8;
preferably, the transition metal source is a water-soluble salt of a transition metal; preferably at least one water-soluble salt of chloride, nitrate and oxalate of transition metal; the preferable transition metal element is at least one of iron, cobalt and nickel;
preferably, the weight ratio of microcrystalline graphite a to transition metal source is 100: 2-10;
preferably, the solvent in the liquid phase vacuum treatment process is water or a homogeneous mixed solvent of water and an organic solvent, wherein the organic solvent is at least one of C1-C4 alcohol and toluene;
preferably, in the liquid phase vacuum treatment process, the solid-liquid ratio is 1: 3-10 g/ml;
preferably, the vacuum degree of the liquid phase vacuum treatment stage is 50-500 Pa;
preferably, the liquid phase vacuum treatment time is 2-6 h;
preferably, the liquid phase vacuum treatment system is subjected to freeze drying treatment to obtain the precursor;
preferably, the atmosphere of the first roasting process is one or more of hydrogen, argon, nitrogen and helium;
preferably, the temperature of the first roasting is 200-400 ℃; the first roasting time is 0.5-2 h.
6. The method of claim 1, wherein the second carbon source is one or more of pitch, phenolic resin, polypropylene, polyacrylonitrile, polypyrrole, glucose, sucrose, polylactic acid, nylon, etc.;
preferably, the weight ratio of the microcrystalline graphite core to the second carbon source is 100: 5-12;
preferably, in the second stage of vacuum roasting, the system is heated to 350-450 ℃ and then set to be in a vacuum state;
preferably, the vacuum degree of the second-stage vacuum roasting is less than or equal to 500Pa, preferably 10-500 Pa, and further preferably 50-300 Pa;
preferably, the temperature of the second-stage vacuum roasting is 900-1250 ℃;
preferably, the time of the second stage of vacuum roasting is 2-6 h;
preferably, the second-stage vacuum roasting product is placed in the treatment liquid for treatment, and then is washed and dried to obtain the microcrystalline graphite/CNT @ C composite material.
7. A microcrystalline graphite/CNT @ C composite material prepared by the preparation method of any one of claims 1-6.
8. Use of a microcrystalline graphite/CNT @ C composite material prepared by the preparation method of any one of claims 1 to 6, characterized in that it is used as a negative active material of a lithium secondary battery;
preferably, it is used as an anode active material to prepare an anode of a lithium secondary battery;
preferably, the negative electrode is used to prepare a lithium secondary battery.
9. A lithium secondary battery negative electrode comprises a current collector and a negative electrode material compounded on the surface of the current collector, and is characterized in that the negative electrode material contains the microcrystalline graphite/CNT @ C composite material prepared by the preparation method of any one of claims 1-6.
10. A lithium secondary battery comprising the negative electrode according to claim 9.
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